Color Blindness (Color About Vision Deficiency) referat
Color Blindness (Color About Vision Deficiency)
What colorblindness is:
Color blindness (color vision deficiency) is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.
Depending on just which figures you believe, color blindness seems to occur in about 8% - 12% of males of European origin and about one-half of 1% of females. I did not find any figures for frequency in other races. Total color blindness (seeing in only shades of gray) is extremely rare.
There is no treatment for color blindness, nor is it usually the cause of any significant disability. However, it can be very frustrating for individuals affected by it. Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray. While this sort of condition is possible, it is extremely rare. Being color blind does keep one from performing certain jobs and makes others difficult.
Life's minor frustrations (and occasional dangers) for the color blind:
Weather forecasts - especially the Weather Channel - where certain colors just can not be distinguished on their weather maps. Also, maps in general because of the color coding on the legends.
Bi-color and tri-color LEDs (Light Emitting Diodes): Is that glowing indicator light red, yellow, or green?
Traffic lights, and worst of all, Caution lights: Color blind people always know the position of the colors on the traffic light - in most states, Red on top, Yellow in the center, Green (or is that blue?) on the bottom. It isn't good when we go to a city or state where they put traffic lights horizontal - it takes a couple of days to get used to that one! But caution lights present an entirely different problem. In this situation there is only one light; no top or bottom, no right or left, just one light that is either red or yellow - but which is it?
Getting in the sun with your girlfriend: So, you're out in the boat or on the beach with your girlfriend and soaking up the rays. But I can't tell until far too late if I'm getting red - or if she is. If I can tell it's red, by that time it's fire engine red and a painful sunburn is already present.
Color observation by others: "Look at those lovely pink flowers on that shrub". My reply, looking at a greenish shrub "What flowers?"
Purchasing clothing: I've got some really neat colors of clothes. Not everyone appreciates them like I do though; they seem to think the colors are strange. I just don't know why!
Kids and crayons: Color vision deficiencies bother affected children from the earliest years. At school, coloring can become a difficulty when one has to take the blue crayon -and not the pink one- to color the ocean.
Test strips for hard water, pH, swimming pools, etc.: A color blind person is generally unable to :
interpret some chemical reactions
see that litmus paper turns red by acid
identify a material by the color of its flame such as lead blue or potassium purple
interpret the chemical testing kits for swimming pool water, test strips for hard water, soil or water pH tests - all of which rely on subtle color differences and a band of similar colors to compare against.
Cooking and foods:
When cooking, red deficient individuals cannot tell whether their piece of meat is raw or well done. Many can not tell the difference between green and ripe tomatoes or between ketchup and chocolate syrup.
Some food can even look definitely disgusting to color deficient individuals. For example, people with a green deficiency cannot possibly eat spinach which to them just look like cow pat. They can however distinguish some citrus fruits. Oranges seem to be of a brighter yellow than that of lemons.
Are you wearing lipstick? Many color blind people cannot tell whether a woman is wearing lipstick or not. More difficult to handle for some is the inability to make the difference between a blue-eyed blonde and a green-eyed redhead.
Clinical information about color blindness:
Cones (color sensitive receptors) containing single visual pigments selective for red, green, and blue light, are present in the normal human eye. Disturbances of color vision will occur if the amount of pigment per cone is reduced or if one or more of the three cone systems are absent.
Although defective color vision may be acquired as a result of another eye disorder, the vast majority of color blind cases are hereditary - present at birth. The gene for this is carried in the X chromosome. Since males have an X-Y pairing and females have X-X, color blindness can occur much more easily in males and is typically passed to them by their mothers.
Color blindness is rooted in the chromosomal differences between males and females. Females may be carriers of color blindness, but males are more commonly affected.
Color blindness is a malfunction of the retina, which converts light energy into electircal energy that is then transmitted to the brain. This conversion is accomplished by two types of photoreceptor cells in the retina: rods and cones.
The cones are responsible for encoding color. Each cone contains structures or visual pigments sensitive to one of three wavelengths of light: red, green, and blue. Normal persons are able to match all colors of the spectrum by mixtures of only three fundamental color sensitivities. Hence, the huge variety of colors we perceive stems from the cone cells' response to different compositions of wavelengths of light.
Defects in color vision occur when one of the three cone cell color coding structures fails to function properly. One of the visual pigments may be present and functioning abnormally, or it may be absent altogether.
For practical purposes, all color-deficient individuals have varieties of red or green deficiency. Blue deficiencies are very rare. Color deficient patients are not completely red or green blind. Compared to persons with normal color vision, they have some trouble differentiating between certain colors, but the severity of the color deficiency is variable.
Color blindness is normally diagnosed through clinical testing. (See the Ishihara color test - the one most common test used) Although there is no treatment for color blindness, most color deficient persons compensate well for their defect and may even discover instances in which they can discern details and images that would escape normal-sighted persons. At one time the U.S. Army found that color blind persons can spot "camouflage" colors where those with normal color vision are fooled by it.
How color blindness works:
The human eye sees by light stimulating the retina (a neuro-membrane lining the inside back of the eye). The retina is made up of what are called Rods and Cones. The rods, located in the peripheral retina, give us our night vision, but can not distinguish color. Cones, located in the center of the retina (called the macula), are not much good at night but do let us perceive color during daylight conditions.
Many people think anyone labeled as "colorblind" only sees black and white - like watching a black and white movie or television. This is a big misconception and not true. It is extremely rare to be totally color blind. There are many different types and degrees of colorblindness, really they are "color deficiencies" since virtually no one is truly blind to all colors.
People with normal cones and color vision are able to see all the different colors and subtle mixtures of them by using cones sensitive to one of three wavelength of light - red, green, and blue.
A mild color deficiency is present when one or more of the three cones functions "poorly". A more severe color deficiency is present when one of the cones does not function at "all" or is missing.
Protanomaly (one out of 100 males):
Protanomaly is referred to as "red-weakness", an apt description of this form of color deficiency. Any redness seen in a color by a normal observer is seen more weakly by the protanomalous viewer, both in terms of its "coloring power" (saturation, or depth of color) and its brightness. Red, orange, yellow, yellow-green, and green, appear somewhat shifted in hue ("hue" is just another word for "color") towards green, and all appear paler than they do to the normal observer. The redness component that a normal observer sees in a violet or lavender color is so weakened for the protanomalous observer that he may fail to detect it, and therefore sees only the blue component. Hence, to him the color that normals call "violet" may look only like another shade of blue.
Under poor viewing conditions, such as when driving in dazzling sunlight or in rainy or foggy weather, it is easily possible for protanomalous individuals to mistake a blinking red traffic light from a blinking yellow or amber one, or to fail to distinguish a green traffic light from the various "white" lights in store fronts, signs, and street lights that line our streets. Do not let them adjust the color on the television, because it will look far to redish or violet for the rest of the family members.
Deuteranomaly (five out of 100 of males):
Let the deuteranomalous person adjust your television and he would add more green and subtract red. He is considered "green weak". Similar to the protanomalous person, he is poor at discriminating small differences in hues in the red, orange, yellow, green region of the spectrum. He makes errors in the naming of hues in this region because they appear somewhat shifted towards red for him - difficulty in distinguishing violet from blue.
From a practical stand point though, many protanomalous and deuteranomalous people breeze through life with very little difficulty doing tasks that require normal color vision. Some may not even be aware that their color perception is in any way different from normal. The only problem they have is passing a color vision test.
Dicromasy - can be divided into protanopia and deuteranopia (two out of 100 males):
These individuals normally know they have a color vision problem and it can effect their lives on a daily basis. They see no perceptible difference between red, orange, yellow, and green. All these colors that seem so different to the normal viewer appear to be the same color for this two percent of the population.
Protanopia (one out of 100 males):
For the protanope, the brightness of red, orange, and yellow is much reduced compared to normal. This dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished. They may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, not on any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible e.g. Pink flowers, reflecting both red light and blue light, may appear just blue to the protanope.
Deuteranopia (one out of 100 males):
The deuteranope suffers the same hue discrimination problems as the protanope, but without the abnormal dimming. The names red, orange, yellow, and green really mean very little to him aside from being different names that every one else around him seems to be able to agree on. Similarly, violet, lavender, purple, and blue, seem to be too many names to use logically for hues that all look alike to him.
Why Roses are Red and Violets are Blue?
Did you ever wonder why you see the colors you do or if other animals see the same colors that you see? We see light that bounces off of things around us. When the light enters our eyes, special cells tell our brains about the light. These cells are called photoreceptors. Light is made of little bits called photons. When the sun shines, trillions and trillions of these little bits of light fall on the earth. The photons bounce off of almost everything and some of them enter our eyes. Those bits that enter our eyes allow us to see. So, where does the color come from? Starting in the 1600s with Sir Isaac Newton, scientists have believed that there are different kinds of photons. Different types give rise to our sense of colors. The different photons are said to have different wavelengths. Sunlight contains all the different wavelengths of photons. The visible wavelength colors can be seen when you look at a rainbow. Raindrops acting as natural prisms produce the colors. How do our photoreceptors work? /a>
Some people have a genetic defect that makes one or more of the cones fail. This condition is known as color deficiency. You may have heard it called color blindness. Color blindness is fairly common, affecting about nine percent of all humans. It is much more common in men than in women. To test for color blindness a special picture called an Ishihara test is used.
SUNLENSES FOR THE COLORBLIND
If there was a lens that could help the colorblind, would you be interested? For the first time, a patented color enhancing laser dye lens coating provides unique benefits to the color deficient person. The new Solaz lenses are now available to improve the color vision of individuals worldwide having this handicap.
Anomalous trichromats comprise the majority, approximately 75%, of those with abnormal color vision. Studies suggest the Solaz color enhancing lenses can help the majority of this group. About 6% of males are anomalous trichromats, virtually all exhibit some combination of red-green deficiency, either deuteranomalia, which is the condition of relative weakness in green discrimination, or protanomalia, which is the condition of relative weakness in the discrimination of red. Interestingly enough, approximately three out of four of the above exhibit more of a weakness toward the green than the red.
Dichromats, representing about 2% of males, have a more severe form of color deficiency. They comprise about 25% of those with abnormal color vision and are unlikely to be helped by our lenses. Females having some kind of color deficiency are approximately 1/2 of 1%.
The term "colorblindness" is really a misnomer for most of those affected, because less than 1 out a 1,000 see in black and white, or shades of gray, and they are called monochromats.
An exciting part of developing the Solaz color enhancing lenses has been the discovery they can aid color deficient subjects in the discrimination of red and green. The Ishihara and Farnsworth test results suggest that the laser dye lenses can help three out of four of colorblind persons. Additionally, the subjective responses and observations by this group in outdoor settings have been quite positive. It is very important to use a quartz halogen light, when taking one or both of the above mentioned tests, so as to best duplicate the spectral qualities of sunlight. A cool white type of fluorescent light used for illumination will not produce beneficial results in most cases, and therefore should not be used.
Solaz sunglasses with solar-powered laser dye coated lenses make colors so bright... so clear... so vivid...that you will hardly believe your eyes!
Discovered by accident and patented after years of research and development, the high-tech lenses we use in our sunglasses provide unique visual benefits so dramatic they must be seen to be believed. You will see an amazing increase in the purity and saturation of colors, with improved contrast as well.
Studies also suggest that these extraordinary sunglasses can improve color perception of red and green in persons with deficient color vision, with colorblind subjects scoring higher on tests when using the lenses.
How is this possible?
Highly pure laser dyes, more costly than gold, are used as a lens coating. Unlike other conventional lens colors or tints, which merely absorb and transmit light, and in the process diminish overall color perception, these dyes are fluorescent and can emit colors over a wide range of wavelengths in the visible. Paradoxically, they simultaneously absorb light and make colors appear brighter. You might expect the lenses to fluoresce externally, but they do not because it is suppressed by the special nature of the coating. A fluorescent-like rendering of color, is however, transmitted through the lens. The name Solaz stands for solar powered laser lens.
These very special compounds have been used primarily in dye lasers for entertainment, as in laser light shows, as spectral sensitizers used in photographic film, as fluorescent probes used in biological stains and for research in areas beyond the limitations of conventional lasers. Now, for the first time, the proven benefits gained from the above technologies have been applied to a sunglass. We believe the difference you experience will be so pleasurable that you may never be satisfied with any other lens again.
Signs and Symptoms
The symptoms of color blindness are dependent on several factors, such as whether the problem is congenital, acquired, partial, or complete.
Difficulty distinguishing reds and greens (most common)
Difficulty distinguishing blues and greens (less common)
The symptoms of more serious inherited color vision problems and some types acquired problems may include:
Objects appear as various shades of gray (this occurs with complete color blindness and is very rare)
Detection and Diagnosis
Color vision deficiency is most commonly detected with special colored charts called the Ishihara Test Plates. On each plate is a number composed of colored dots. While holding the chart under good lighting, the patient is asked to identify the number. Once the color defect is identified, more detailed color vision tests may be performed.
There is no treatment or cure for color blindness. Those with mild color deficiencies learn to associate colors with certain objects and are usually able to identify color as everyone else. However, they are unable to appreciate color in the same way as those with normal color vision.
We humans are all born colorblind! The cones don't begin functioning until a baby is about 4 months old. At that time the baby undergoes a gradual transformation that is as remarkable as the scene in the Wizard of Oz when Dorothy leaves the black-and-white world of Kansas for the brilliant colors of Oz. About one out of 40,000 babies never develops cones, seeing only in black-and-white throughout life. This is called achromatopsia, or rod-monochromatic colorblindness.
There are many other versions of colorblindness, but by far the most common is red-green colorblindness, which affects as many as one out of 25 people. These people either do not have red cones (protanopia) or green cones (deuteranopia). They are unable to distinguish between green and red, but with their remaining two types of cones are able to see all of the other colors. The absence of blue cones is extremely rare. Colorblindness is usually tested for at children's four-year physicals. The doctor asks them to identify a red and a green line on the eye chart. If any question remains, more precise visual testing can determine the exact nature of the problem.
While normally rare, complete color blindness (maskun) is very common in Pohnpei; about 1/12 of the population there has maskun.
Color Vision. Statistics
· 1 in 12 people have some sort of color deficiency. About 8% of men and 0.4% of women in the US.
· 0.38% of women are deuteranomalous (around 95% of all color deficient women).
· 0.005% of the population are totally colour blind.
· 0.003% of the population have tritanopia. 33823vef76qdi2b
· Protanomaly occurs in about 1% of males.
· Deuteranomaly occurs in about 5% of males. It's the most common color deficiency.
· Protanopia occurs in about 1% of males.
· Deuteranopia occurs in about 1% of males. ed823v3376qddi
Ishihara Test for Color Blindness
What numbers do you see revealed in the patterns of dots below?
Normal Color Vision
Red-Green Color Blind
New Pediatric Color Vision Test For Three to Six Year Old Pre-School Children
by Dr. Terrace L. Waggoner
Several years ago my son T.J., who was six years old at the time, came home from school with a note from the school nurse saying he was "Colorblind".
Being an optometrist, I should have already known he had a color deficiency. I thought back to when T.J. was in pre-school and kindergarten. His teachers mentioned he was having difficulty learning concepts such as grouping same or different colored objects. I thought it was a learning problem. I did not think it could be a visual problem because at age 4, before he started pre-school, I had T.J. given a complete eye examination by a pediatric eye doctor who was a friend of mine.
I told my friend about the note from the school nurse. She confided that she didn't test the color vision of pre-school children because of time restraints and the difficulty of testing such a young age group. This is the case with most vision care professionals, and why I developed "Color Vision Testing Made Easy".
The new pediatric pseudoisochromatic (different colored dots) color vision test contains 14 plates. The simple objects (circle, star, square) and pictures (boat, balloon, dog) make color vision testing fun, quick and easy for all age groups - especially 3 to 6 year old pre-school children.
Susan Cotter, O.D. (Pediatric Specialist, Southern CA College of Optometry) and David Lee, Ph.D, O.D. (Color Vision Specialist, Illinois College of Optometry) completed a validation study of Color Vision Testing Made Easy. They proved it was a valid color vision test and 100% Ishihara compatible. Testability of kindergarten children was 100% with no false positives.
Color Vision Testing Made Easy was also used in a special study by Graham Erickson, O.D. (Pacific University College of Optometry) and Sandra Block, O.D. (Illinois College of Optometry) to test the color vision of Special Olympic Athletes in the 1997 World Winter Games in Toronto, Canada; the Regional European Swim Competition in Spain; and the Summer Games in Texas and Massachusetts, USA. They demonstrated the new color vision test, because of it's simplicity, could be used to detect color deficiencies in mentally handicapped patients. The study was sponsored by the American Optometric Association Sports Vision Section and Special Olympic International.
Inexpensive pediatric color vision test that makes testing fun, quick, and easy for "all" age groups - especially 3 to 6 year old pre-school children.
Comprehensive 100% Ishihara compatible with 14 pseudoisochromatic test plates.
Easily identified objects by children as young as three - circle, star, square, boat, dog, and balloon.
Only takes a minute to administer and score - making it invaluable for any size vision screening.
Children do "not" need to know their numbers.
Built-in check confirms children are trying their best - you will be confident with your diagnosis.
Professor Holmgren’s Test For Color Blindness
(Holmgren-Thompson Wool Test for Colour - Blindness)
Maker, source: American Optical Company, Southbridge, Pennsylvania Year made, acquired: c. 1900
l x w x h; 27 x 12 x 4 cm markings on standards: green "A"; purple "B"; red "C".
Each wool skein has a brass plate with a number marking "1", "2" "3" etc., with a moveable brass disc to cover the number.
Instructions pasted on inside of box:
Holmgren-Thompson wool test for colour-blindness.
Place the 40 small skeins together. Keep the tags covered.
Select the 10 skeins that best match the light green master A.
Next, from the remaining thirty, select the 5 skeins that best match the red master, C.
Finally, from the remaining twenty-five, select the 5 skeins that belong with the rose master, B.
Record the tag numbers of each selection set, arranging them in order of closest match to the respective master skeins
Students at the University of Toronto used the Holmgren Wool test for laboratory exercises. Physicians and laymen used the test primarily for the detection of colour-blind employees of railway and shipping lines. A set of instructions (most likely added at the University of Toronto) were pasted inside the front lid of the container (see above). These instructions are very similar to a variation of Holmgren’s test designed by Dr. William Thomson, a Philadelphia ophthalmologist. The test kit consists of three test worsteds and forty match and confusion worsteds. The subject was asked to match the worsteds with the test wool. If she chose the confusion colours instead of the proper match colours, the subject was said to be colour blind. For example, with the Pink Test worsted, if the subject chose blue or violet, the subject would be termed red-blind. If she chose green or gray, the subject was said to be green-blind.
Fithiof Holmgren (1831-1897), the inventor of the above test, was a Swedish physiologist who made his reputation studying the retina’s electrical response to light. Early in his career, Holmgren studied under Herman von Helmholtz and Emil DuBois-Reymond. The success and popularity of Holmgren’s original test owed as much to his innovation as to the context of his work. Holmgren’s original test was directly inspired by a well-publicized railway accident at Lagerlunda, Sweden, in 1876. Holmgren suspected that the engineer of the train suffered from colour-blindness and he set out to test this theory by examining 266 employees of the Uppsala-Gabole line. As he suspected, thirteen of these employees were found to be colour blind. Holmgren’s test quickly established itself as a systematic, reliable way of detecting colour blindness in railway and shipping employees.
The original Holmgren test of 1879 was the first successful attempt to standardize the detection of colour-blindness. Seebeck and Wilson had made a similar attempt in the 1850’s but their efforts were ignored and forgotten (Boring, 1942). Holmgren based his test on the Young-Helmholtz theory of colour perception which stated that there were three sets of colour perceiving elements in the retina. According to the theory, a defect in one of these elements caused a variant of colour-blindness. Holmgen designed the test to require matching, rather than naming of colours. The original test was more cumbersome than the kit used by U of T students; it had over 160 wools: 3 test colours, and 20 match and confusion colours, (8 shades each).
Dr. William Thomson devised his test under similar circumstances. In 1879 the American government commissioned Thomson to devise a colour-blind test for railway and shipping employees. Thomson worked to simplify Holmgren’s method so that a "non-professional" could conduct the testing and transmit the results to an expert for interpretation. In a series of variations to Holmgren’s test, Thomson reduced the number of matching colours, and numbered the worsteds.
Much of the success of the Holmgren-Thomson test can be attributed to the simplicity and portability of its design. This test represents one of the earliest examples of a psychological test used on a large group of people.
How can teachers help if a child has a color deficiency?
a. Label a picture with words or symbols when the response requires color recognition.
b. Label coloring utensils (crayons, colored pencils, and pens) with the name of the color red.
c. Use white chalk, not colored chalk, on the board to maximize contrast. Avoid yellow, orange, or light tan chalk on green chalkboards.
d. Xerox parts of textbooks or any instructional materials printed with colored ink. Black print on red or green paper is not safe. It may appear as black on black to some color deficient students.
e. Assign a classmate to help color deficient students when assignments require color recognition. Example - color coding different countries on a world map.
f. Teach color deficient students the color of common objects. Knowing what color things are can help them in their daily tasks. Example: when asked to color a picture, they will know to use the crayon "labeled" green for the grass, blue for the sky, and light tan for Lincoln's face.